Abstract
Experiments simulating intense vortices associated with tornadoes that occurred on 6 May 2012 on the Kanto Plain, Japan, were performed with a nested local ensemble transform Kalman filter (LETKF) system. Intense vortices were reproduced by downscale experiments with a 12-member ensemble in which the initial conditions were obtained from the nested LETKF system analyses. The downscale experiments successfully generated intense vortices in three regions similar to the observed vortices, whereas only one tornado was reproduced by a deterministic forecast. The intense vorticity of the strongest tornado, which was observed in the southernmost region, was successfully reproduced by 10 of the 12 ensemble members. An examination of the results of the ensemble downscale experiments showed that the duration of intense vorticities tended to be longer when the vertical shear of the horizontal wind was larger and the lower airflow was more humid. Overall, the study results show that ensemble forecasts have the following merits: (1) probabilistic forecasts of the outbreak of intense vortices associated with tornadoes are possible; (2) the miss rate of outbreaks should decrease; and (3) environmental factors favoring outbreaks can be obtained by comparing the multiple possible scenarios of the ensemble forecasts.
Highlights
Local heavy rainfalls and tornadoes cause severe damage due to flash floods, landslides, and strong winds
Intense vortices produced by the inner local ensemble transform Kalman filter (LETKF) and NHM-350 NHM-350 successfully reproduced the rainfall regions from 11:00 Japan Standard Time (JST) to 12:00 JST, which includes the period of the intense vortices associated with the tornadoes (Fig. 6)
Intense vortices, where vertical vorticity exceeded 0.1 s−1 at 12:00 JST, were located near the southern tip of the rainfall regions generated by ensemble members #000, #002, #003, #004, and #008; this position corresponds to that of the southernmost tornado generated in intense rainfall region I (Fig. 3)
Summary
Local heavy rainfalls and tornadoes cause severe damage due to flash floods, landslides, and strong winds. Forecasts of convection cells generated in areas of weak convergence, which frequently occur in urban areas such as the Tokyo Metropolitan Area in summer, are affected by small errors in the initial conditions. This means that forecasts of the position and timing at which a thunderstorm will be generated from a weak convergence are. The ensemble forecasts operationally performed by the Japan Meteorological Agency (JMA) with the highest horizontal resolution are typhoon forecasts and 1 week forecasts These ensemble forecasts cannot represent convection cells of thunderstorms that cause local heavy rainfall and tornadoes because the horizontal grid interval (40 km) is too large to resolve the convection
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
